The present invention relates to a continuous process for the manufacture of carboxylic peracids by reaction of the corresponding carboxylic acids with hydrogen peroxide in the presence of a catalyst.
It is known to manufacture carboxylic peracids by reacting the corresponding carboxylic acid with hydrogen peroxide, generally employed in the form of an aqueous solution, in the presence of small amounts of a catalyst such as sulphuric acid. This reaction gives rise to the formation of water. In order to obtain the carboxylic peracid directly in the anhydrous form, it has been proposed, in U.S. Pat. No. 2,814,641 issued to Phillips et al on Nov. 26th, 1957, to carry out the reaction in the presence of a solvent which is capable of forming a minimum boiling-point azeotrope with water, and to remove the water formed by the reaction, and also the water for dilution of the reactants, by distillation of this azeotrope.
This known process exhibits certain serious disadvantages. In fact, the proportion of peroxide compounds (hydrogen peroxide and carboxylic peracid) present in the reaction mixture is very large and increases as the reaction and the azeotropic distillation proceed. This involves risks of explosion which make the reaction particularly difficult to carry out. Furthermore, in this known process, the catalyst is present in the organic solution of peracid at the end of the process and it is therefore necessary to provide for the removal of this catalyst. This removal is extremely difficult to carry out. Furthermore, the presence of spent catalyst in the organic solution of peracid proves very inconvenient for all the subsequent uses of this solution, such as its use as an epoxidizing agent. Moreover, this process involves a high consumption of catalyst which cannot be recovered. Thus, in order to limit the disadvantages associated with the presence of the catalyst in the organic solution of peracid, it is necessary to use small relative amounts of catalyst, which generally do not exceed 5% of the weight of carboxylic acid employed, and this has the adverse consequence of substantially reducing the reaction rates. Finally, since the reaction for the formation of the peracid takes place mainly in the aqueous phase and, furthermore, since this aqueous phase is removed by azeotropic distillation, the rate of production of the peracid decreases very substantially with time as the aqueous phase disappears. In order to achieve high degrees of conversion, it is therefore appropriate to use very long reaction times. Thus, it is only with great difficulty that this known process can be carried out in installations which operate continuously.